Quadrajet idle issues.

[Awann99]

I have a rebuilt Quadrajet from National carbs one my 350 with a Sp2p intake and ram horn exhaust. Nothing fancy. Just something to daily drive. I have been having issues with the carb every few months we’re it floods out and spews gas out of every nook and cranny and won’t start. I’ll usually pull the fuel line off and run it dry buy turning it over and then it runs fine. The flooding usually foals the spark plugs as well so I change those. Now it runs extremely poorly. The idle is around 550 and it shakes like it has a vacuum leak but I haven’t found one. After it’s starts driving it preformed fine. Strangely after driving for about 15 minutes when I stop it will idle at 700-800 rpm for the rest of the time it’s running. Maybe a choke issue? It’s a non divorced electric choke. National Carbs said they will take it back and work on it because it sounds like a stuck float. But I wanted to see what you guys thought so I could better understand what going on and fix it myself if this happens again. Also the throttle has a tight spot. After a small amount of pedal it wants to hang up and you gotta kinda force it to get it to kick in.
Thank you.

[lil hoodlum]

Sorry, I'm not into some abbreviations but what is a Sp2p intake?

[body bolt]

If it's spewing fuel the float/needle/seat isn't doing its job.

[Awann99]

Originally Posted by lil hoodlum

Sorry, I'm not into some abbreviations but what is a Sp2p intake?

It’s an old edelbrock intake that has long been discontinued. It was made for low rpm torque and fuel economy. I’ll attach a photo.

[Awann99]

Originally Posted by body bolt

If it's spewing fuel the float/needle/seat isn't doing its job.

Could this cause it to give off the rough idle as well? I’ll do some searches over how it works so I can get a better understanding of it.

[Wrenchbender Ret]

You are getting foreign material in the carb. At first it was holding the needle open. Now it has aqumulated enough to clog up some passages. You need a good filter to catch it before it gets to the carb. You should pull the tank & clean it or get a new tank.
George

[YellowK5]

Agree with wrenchbender..make sure the fuel system is clean and you have a good filter installed...The float is sticking or the needle and seat is sticking open...yes it will run like crap when this happens

[Tomchev]

Trash under the needle are to much fuel pressure.

[dmjlambert]

Do you periodically remove and replace the fuel filter that is built into the carburetor fuel inlet, and do you find any particles or dirt in it? You need to be careful with the inlet fuel filter access and don't cross thread it. Treat it with care, and put a new filter gasket on every time or every other time you change the fuel filter. Make sure the filter spring is in there behind the fuel filter. You can get new fuel filters at car parts stores and they are very inexpensive. I recommend sending the carburetor back to National Carburetor, they may cover it on warranty.

[rockyrivermark]

Check your fuel pressure also

[Caddylackn]

x2 on the fuel pressure. A quadrajet's fuel operating pressure should be 4-6 psi, or it will let fuel past the needle seat around 7 psi.

Or if your fuel pressure is within spec, you could have a float that has a hole or the nitrophyl float is fuel soaked and needs replaced. There are aftermarket brass floats available.

You can swap out to a later model float system (later 70s quadrajet) that uses a different fulcrum point on the float to get more leverage on the needle seat with a smaller float size. The floats are smaller so it has more fuel capacity in the bowl as well.

[Awann99]

UPDATE: I just got back from a vacation. The truck ran like crap. I dumped a can a sea foam in the tank and sprayed the b12 carb cleaner stuff all over the carb and down the throat while it was running crappy and it eventually idled out and ran smooth. Tach reads 650 rpm. I’m going to pull it off and send it back to Nat Carbs anyway like y’all suggested. It is a custom carb they made for me. I believe 1984 style so I have an electric choke with 69-72 throttle arms. I’m going to add a inline fuel filter behind my fuel pump and after my line exists the cab just to be safe. The tank will be replaced soon. Should a I get a 1972 style and add all the ECC stuff to help eliminate the gas build up in the tank? Every “vented” gas cap I get doesn’t work. Also the carb filter was never dirty when I pulled it open that I could tell. I was also very careful to not strip it.
Thank you all for the help.